An intraocular lens (IOL) is an optical device which is implanted into the anterior chamber (i.e., anterior to iris) or posterior chamber of the eye to replace the natural crystalline lens damaged by cataract, injury, etc.
IOLs are usually made mostly of clear arcylic resin (polymethylmethacrylate or PMMA), a rigid, glassy polymer. Since the PMMA IOL is about 6 mm in diameter in the narrowest axial cross-section (i.e., the plane including optical axis), the incision has to be appropriately large.
New surgical techniques and instruments allow for removal of the cloudy natural crystalline lens (i.e., cataract) through a much smaller incision than 6 mm (typically 2-3 mm). The major advantages of the small incision are lesser trauma, lower loss of intraocular pressure and aqueous humor during the surgery, easier healing and lesser risk of astigmation due to scar contraction.
In addition, these techniques (e.g., facoemulsification) permit only partial removal of the lens. Only the opacified geleous substance need be removed, while the lens capsule, or at least its posterior part, is left intact. The lens capsule is then utilized to keep the IOL in the proper location or, it can be even refilled by a suitable medium to restore its optical function.